The Senate began debating a far-reaching bill Thursday to overhaul financial regulations, bracing for a series of amendments in coming days that will highlight key divisions between Democrats and Republicans.

The first proposed amendment, introduced by Sen. Barbara Boxer (D-Calif.), would prohibit using any more taxpayer money to bail out troubled financial companies. This goal is so widely shared that members of both parties have been tripping over one another to assure the public that they are best at safeguarding taxpayers' wallets. But like other goals in the legislation that are widely shared by both parties, disputes remain over how best to do it.

After blocking the bill's progress for three days in hopes of hammering out a bipartisan compromise behind closed doors, Republicans this week allowed the bill to move on to floor debate when negotiations between Sen. Christopher J. Dodd (D-Conn.) and Sen. Richard C. Shelby (R-Ala.) again reached an impasse.

Lawmakers now face the prospect of two weeks or more of debate on the bill, which would create a new consumer regulator, establish oversight of the vast derivatives market and give the government authority to wind down large, troubled financial companies without leaving taxpayers on the hook.

"The status quo is unacceptable," Dodd, the chief architect of the bill, said on the Senate floor on Thursday. "We cannot leave the American people vulnerable to the present construct of our financial regulatory system."

The real fight over the details of the legislation will begin to unfold next week, as lawmakers on Tuesday begin voting on additional amendments.

Dodd and Senate Majority Leader Harry M. Reid (D-Nev.) have vowed a fair and open amendment process. Still, Democratic leaders must walk a fine line as they try to pick up one GOP vote -- and maybe more -- to reach the 60 needed to overcome the threat of a filibuster.

On one hand, they must allow consideration of a wide range of amendments, particularly from Republicans, to make good on their promise of a full-throated debate. On the other, leaving the door open to too many amendments could lead to potentially endless quibbling and fundamentally alter parts of the legislation. In addition, they must navigate the minefield of amendments in a charged political environment during an election season, gaining GOP support without losing Democrats along the way.

Reid and Minority Leader Mitch McConnell (R-Ky.) have yet to agree to the specific number of amendments that will be allowed or the order in which they will be heard. Democratic and Republican aides said Thursday that members had only begun to file amendments.

If recent history is any indication, a flood of proposals lie ahead. Republicans on the banking committee submitted hundreds of amendments when the bill came up for consideration in March. At the time, Shelby decided against introducing any amendments in committee, choosing to continue talking with Dodd behind closed doors.

Although the proposed changes to Dodd's bill are certain to run the gamut of issues, several topics are likely to dominate the debate.

Dodd's bill would create a powerful, independent consumer financial protection bureau within the Federal Reserve to oversee mortgages, credit cards and other such loans. Republicans have long opposed the new consumer agency, insisting it would have too much power and could harm small businesses, stifle innovation and raise consumer costs.

Shelby and other Republicans, such as Bob Corker of Tennessee, said they plan to introduce amendments to scale back the power and scope of the consumer regulator. Meanwhile, Sen. Jack Reed (D-R.I.) plans to push for a standalone consumer agency.

Lawmakers also are certain to wrangle over the details of proposed rules to rein in the $600 trillion market in financial derivatives, including provisions that could force banks to spin off their derivatives desks and measures that would require nearly all deals to be traded openly on exchanges. Shelby has said the language in the Dodd bill, drafted largely by the agriculture committee's chairman, Sen. Blanche Lincoln (D-Ark.), "would have far-reaching and devastating effects" by raising costs for businesses that use derivatives to manage risk, such as the fluctuating price of oil, rather than simply speculating.

Republicans and Democrats also must settle differences over the "resolution authority," which would empower regulators to wind down large, troubled firms without using taxpayer money. Republicans have argued that the current bill doesn't accomplish that goal. In part to allay their concerns, Democrats have agreed to drop a proposed $50 billion fund paid for by the financial industry that would go to shutting down failing companies.

Other amendments currently circulating could cause major waves in the financial world.

For instance, Sens. Ted Kaufman (D-Del.) and Sherrod Brown (D-Ohio) are pushing legislation to break up big banks. Sens. Jeff Merkley (D-Ore.) and Carl M. Levin (D-Mich.) introduced an amendment that, among other things, would ban banks from making speculative investments using their own capital -- an activity known as proprietary trading -- and from owning a hedge fund or private-equity fund. Sens. Maria Cantwell (D-Wash.) and John McCain (R-Ariz.) are pushing to re-introduce the Glass-Steagall provision, repealed in 1999, that separates commercial from investment banking.

Whatever bill emerges from the Senate must be squared with the one the House passed in December. Administration officials and Senate staff members have been briefing Rep. Barney Frank (D-Mass.), with the goal of making that process as smooth as possible.